This application claims priority of Taiwan patent Application No. 090208444, filed on May 23, 2001.
1. Field of the Invention
The invention relates to a directional tap, more particularly to a directional tap with a surge protection capability.
2. Description of the Related Art
FIG. 1 illustrates a conventional directional tap 1 that includes a base 11, a splitting circuit board 12 disposed in the base 11, and a cover 10 mounted removably on the base 11. The base 11 is formed with input and output ports 110, 112. The input port 110 is provided with an input connector 13. The output port 112 is provided with an output connector 14. The input and output ports 110, 112 are connected electrically to a cable television network via cables 20 for receiving and outputting a video signal. The cover 10 is formed with a plurality of directional output terminals 100, each of which is connected to a client end via a respective cable 21 for outputting a distributed video signal from the splitting circuit board 12 and corresponding to the video signal received at the input port 110.
The conventional directional tap 1, which is generally installed in outdoors, may experience a voltage surge when lightning strikes. It is noted that a surge voltage larger than 2 KV and present in the video signal and the distributed video signal can result in damage to the conventional directional tap. In a conventional directional tap, a varistor, a bi-directional switch, a gas tube or the like is used to bypass surge voltages present in the video signal and the distributed video signal for surge protection. For example, an inexpensive varistor (about 0.5 USD/piece) has an instantaneous current load of about 100 Amps, whereas an expensive varistor (about 10 USDs/piece) has an instantaneous current load of about 3000 Amps or more. As such, the surge protection effect depends on the price of the varistor. In order to provide superior surge protection, the conventional directional tap encounters the drawback of relatively high costs.
Therefore, the object of the present invention is to provide a directional tap that offers a surge protection function at a relatively low cost.
According to the present invention, a directional tap comprises:
input and output ports adapted to be connected electrically to a cable television network for receiving and outputting a video signal;
a splitting circuit having an input connected electrically to the input port, an output connected electrically to the output port, and a plurality of directional output ends, the splitting circuit receiving the video signal from the input port and outputting a distributed video signal corresponding to the video signal from the input port at each of the directional output ends;
a plurality of directional output terminals, each of which is connected electrically to a respective one of the directional output ends for outputting the distributed video signal to a client end; and
a plurality of surge protection circuit units, one of which is connected between the input port and the input of the splitting circuit, the remaining ones of which are connected between a respective one of the directional output ends of the splitting circuit and a respective one of the directional output terminals, the surge protection circuit units bypassing surge voltages present in the video signal and the distributed video signal, each of the surge protection circuit units including an inductor having a first terminal connected electrically to the splitting circuit, and a second terminal cooperating with a ground terminal to define a gap.